High surf will pummel the Southern California coastline Wednesday and Thursday, the result of large swells created by storms spreading from the northern Pacific and sparking dangerous conditions along the beaches of Los Angeles and Orange counties, according to forecasters.

A high surf advisory in L.A. County that went into effect at 4 a.m. will last through 8 p.m. Thursday. The advisory for Orange County will last from 10 a.m. Wednesday through 10 p.m. Thursday.

Powerful winds from several northern Pacific storms drove the high surf, National Weather Service meteorologist Curt Kaplan said. Waves of 6 to 12 feet are expected along the Southern California coast, while 17- to 22-foot surf may break north of Point Conception, he said.

Farther to the south, in San Diego County, a powerful winter swell was generating 6- to 12-foot waves. The swell already had led to the closure of the Ocean Beach Pier in San Diego.

A hazardous surf advisory there will be in place until 10 p.m. Thursday.

The Ventura County Pier was also preemptively closed Wednesday because of high surf, the Police Department announced on Twitter. The pier was closed last month after powerful waves snapped at least one piling of the 146-year-old landmark.